From Wolf Tooth:

Medium Strap and Accessory Mount allows you to carry accessories on your bike frame instead of in jersey pockets or backpack

• Securely strap 2-3.25" diameter items like CO2 cartridges, tubes, jackets, bags, and more

• Lightweight, durable, rust-proof materials

• Includes the mounting plate, strap and associated ED-coated hardware

Compatibility

• Mounts directly to the braze-ons on your frame using the included spacers. A B-RAD base is recommended if you want to adjust the mount's position along the frame tube or mount a bottle inline above it.
• Compatible with any frame that uses standard 64mm spacing bottle cage braze-ons (basically every modern frame)
• Securely straps items 50-80mm in diameter
• Hardware included is T25 Torx head

• Extremely grippy and flexible strap with reflective tab and foam pad